With the development of the science and technology, new energy vehicles, especially electric vehicles, gradually enter into ordinary families as a means of transportation. The performance requirement, especially the comfort requirement of a user for the vehicle, is higher and higher, which requires that the vehicle must adapt to different operating requirements. But currently most electric vehicles cannot satisfy such requirements. Especially in winter, the temperature is low so that the capability of the battery, no matter the discharge capability or the battery capacity, may be decreased or the battery cannot even be used.
Specifically, the work temperature of the battery especially a lithium ion battery is generally within a range from −20° C. to 55° C., and the battery is not allowed to be charged at a low temperature. Under a low temperature condition, the battery in the electric vehicle may have the following problems: (1) The lithium ions may be deposited easily at the negative electrode and lose the electrical activity at the low temperature, and therefore, if the battery in the electric vehicle is frequently used at the low temperature, the life of the battery may be shortened and a safety problem may be caused accordingly. (2) When the lithium ion battery is charged at the low temperature, the lithium ions may be deposited easily at the negative electrode to become dead ions and thus the capacity of the battery may be decreased. Moreover, the deposited ions grow larger and larger during the continuous use, thus leading to a potential danger such as an internal short circuit. (3) The discharge capability of the battery is limited at the low temperature. All of the problems listed above may be not favorable for the electric vehicle which uses green and environment friendly new energy.
The method for heating a battery is an important technology in the electric vehicle field. A heating strategy of the battery and the performance of the battery heater influence the comfort, operation stability and safety of the vehicle directly. Many new technologies are applied in the battery heating, but because of the self-capability defects, these technologies are not widely applied in the vehicle field. For example, a thermal insulation sleeve is provided to warm a battery by thermal insulation material; an infrared radiation film is used to heat the battery and a thermal insulation sleeve is provided to keep the battery warm; or a heating patch is attached on the surface of the battery. These methods are only suitable for the fixed battery. For a pure electric vehicle, the use of a huge heating system increases the weight of the entire vehicle, thus increasing the energy consumption of the vehicle. Furthermore, using the external power to heat the battery is not suitable for the vehicle which is not fixed in position. Therefore, the above methods have not been widely applied in the electric vehicle field.